Contents

Fiction

Generation 1 cartoon

When Megatron lead the Decepticons on a raid of Sherman Dam, Megatron and Optimus Prime battled on the top of the dam. As the Autobot leader brought out his energon-axe, Megatron revealed his energon mace. After some obligatory trash talking, Megatron and Prime proceeded to thrash each other. However, Megatron only won when Prime's attention was turned to Spike Witwicky calling for help, allowing Megatron to knock Prime off the dam, and fly away with the Decepticons. More Than Meets the Eye, Part 2

Full Throttle Scramble Power!

After having his latest weapon, the Omega Whip, destroyed by a mind-controlled Starscream, Megatron found his means of escape blockaded by his nemesis, Optimus Prime. Megatron swiftly unleashed his energon mace, tangling his foe in its powerful chain. Megatron's upper hand in combat did not last long, as Optimus was soon rescued from the confrontation when Metroplex arrived on the scene and scared all the Decepticons away, including Megatron. Full Throttle Scramble Power!

Marvel Comics continuity

TBD

Dreamwave continuity

Eons ago, when Optimus Prime and Megatron were fighting in the bowels of Cybertron, Megatron breached the casing on the Matrix, causing the two Transformers to see visions of the future. Among them were Prime and Megatron fighting with their respective Energon weapons on Earth. The War Within issue 5

Movie

This weapon is first revealed when Megatron wakes up from his deep-freeze inside the Hoover Dam. After awakening and announcing his true name, he proceeded to destroy the surrounding area with his energon mace, then transformed and flew out through a large culvert in front of him.
At the Battle of Mission City, Megs used his mace to knock Sam off of the building and make him fall to his doom for refusing to give him the All Spark.